One table or many in shop database

I'm going to be creating an ecommerce site soon, database driven, php mySQL, with potentially a couple of hundred members.

Do I create one big table with all the members items in, or do I create a table per member? Each member will sell between 10 - 60 items.

If I create a table per member how will this affect a database search facility? I imagine it would be easier to create a search that queries one main table rather than many? Or will one big table be slower to search?

I use WebAssists eCart software which I find pretty useful and easy to integrate. I've written shops before where there has been only one store, and have used relational databases to some extent, basically in the way outlined in harristweed's post. However there has only been one "owner", ie, that of the store itself.

In this case I have several owners and want to be sure that I can ensure privacy. Having one big table and giving each member limited access to edit or add products under their own "member_ID" field only is one solution, but I was worried that by simply changing a php query in the web browser from "store.php?ID=1234" to "store.php?ID=1235" the user could potentially edit someone elses details maliciously.

I figured that perhaps giving each member their own table may help combat this, but this may complicate the search facility.